To see the other types of publications on this topic, follow the link: FW-H equation.
Journal articles on the topic 'FW-H equation'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'FW-H equation.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Kusyumov, Alexander, Sergey Mikhailov, Sergey Kusyumov, Elena Romanova, and Georgios Barakos. "Some Peculiarities of Helicopter Main Rotor Aeroacoustic for Far-Field Observer." EPJ Web of Conferences 213 (2019): 02048. http://dx.doi.org/10.1051/epjconf/201921302048.
Full textAbstract:
Mathematical models for helicopter rotor acoustics are usually based on the Ffowcs Williams–Hawkings (FW–H) equation. The level of rotor noise is determined by geometry (thickness noise) of a flying vehicle and distributed blade loading (loading noise). Initially, the FW-H equation was obtained from Euler’s equations and does not depend on the viscosity of flow. In the present work the UH-1H helicopter is considered as a test case for numerical CFD simulation and comparison to experimental data.
2
Tao, Jun, Gang Sun, Ying Hu, and Miao Zhang. "Noise Prediction for Multi-Element Airfoil Based on FW-H Equation." Applied Mechanics and Materials 52-54 (March 2011): 1388–93. http://dx.doi.org/10.4028/www.scientific.net/amm.52-54.1388.
Full textAbstract:
In this article, four observation points are selected in the flow field when predicting aerodynamic noise of a multi-element airfoil for both a coarser grid and a finer grid. Numerical simulation of N-S equations is employed to obtain near-field acoustic information, then far-field acoustic information is obtained through acoustic analogy theory combined with FW-H equation. Computation indicates: the codes calculate the flow field in good agreement with the experimental data; The finer the grid is, the more stable the calculated sound pressure level (SPL) is and the more regularly d(SPL)/d(St) varies.
3
Najafi-Yazdi, Alireza, Guillaume A. Brès, and Luc Mongeau. "An acoustic analogy formulation for moving sources in uniformly moving media." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, no. 2125 (June 30, 2010): 144–65. http://dx.doi.org/10.1098/rspa.2010.0172.
Full textAbstract:
Acoustic analogy methods are used as post-processing tools to predict aerodynamically generated sound from numerical solutions of unsteady flow. The Ffowcs Williams–Hawkings (FW–H) equation and related formulations, such as Farassat’s Formulations 1 and 1A, are among the commonly used analogies because of their relative low computation cost and their robustness. These formulations assume the propagation of sound waves in a medium at rest. The present paper describes a surface integral formulation based on the convective wave equation, which takes into account the presence of a mean flow. The formulation was derived to be easy to implement as a numerical post-processing tool for computational fluid dynamics codes. The new formulation constitutes one possible extension of Farassat’s Formulation 1 and 1A based on the convective form of the FW–H equation.
4
Seol, Hanshin, Cheolsoo Park, and Ki-Sup Kim. "Numerical Prediction of Marine Propeller BPF Noise Using FW-H Equation and Its Experimental Validation." Transactions of the Korean Society for Noise and Vibration Engineering 26, no. 6_spc (November 20, 2016): 705–13. http://dx.doi.org/10.5050/ksnve.2016.26.6.705.
Full text
5
Lyrintzis, Anastasios S. "Surface Integral Methods in Computational Aeroacoustics—From the (CFD) Near-Field to the (Acoustic) Far-Field." International Journal of Aeroacoustics 2, no. 2 (April 2003): 95–128. http://dx.doi.org/10.1260/147547203322775498.
Full textAbstract:
A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-field CFD results to the acoustic far-field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface Ffowcs-Williams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field CFD data. Both methods can be extended in order to include refraction effects outside the control surface. The methods have been applied to helicopter noise, jet noise, propeller noise, ducted fan noise, etc. A simple set of portable Kirchhoff/FW-H subroutines can be developed to calculate the far-field noise from inputs supplied by any aerodynamic near/mid-field CFD code.
6
Chen, Li, Yang Yu, and Guo Xiang Hou. "Flow-Induced Noise Radiation from the Rotational Bodies Based on Fluid Mechanics Using Hybrid Immersed Boundary Lattice-Boltzmann/FW-H Method." Applied Mechanics and Materials 345 (August 2013): 345–48. http://dx.doi.org/10.4028/www.scientific.net/amm.345.345.
Full textAbstract:
A novel study of the simulations of the flow-induced noise from the moving boundary objects using the hybrid immersed boundary lattice-Boltzmann method (IB-LBM), which is the modern useful numerical method of fluid mechanics, on the Ffowcs Williams-Hawkings (FW-H) equation is carried out. The permeable surface FW-H method has been demonstrated an effective technique of the far-field noise predication, because of its complete theories and successful applications in aeroacoustics. It usually need the information of the field near sound source. Therefore, we also adopt the effective and widely used IB-LBM to treat the interaction of the moving boundaries and the fluid, in order to simulate the near-field accurately. Some simulations are shown to test the hybrid method, including the rotational cylinder. The results prove that the hybrid IB-LBM/FW-H method can simulate the large field problems of the flow-induced noise effectively and accurately.
7
Guo, H., YS Wang, F. Zhu, NN Liu, and C. Yang. "Multi-field coupling prediction for improving aeroacoustic performance of muffler based on LES and FW-H acoustic analogy methods." International Journal of Aeroacoustics 20, no. 3-4 (March 24, 2021): 414–36. http://dx.doi.org/10.1177/1475472x211005409.
Full textAbstract:
Based on the large eddy simulation (LES) and Ffowcs Williams and Hawkings (FW-H) equation, a multi-field coupling method is presented for aeroacoustic prediction of a muffler with high-speed and high-temperature exhaust gasflow. A three-dimensional finite-volume model of the muffler is established by using the LES and FW-H acoustic analogy (FW-H-AA) methods. Experimental validations of the simulated results suggest a good accuracy of the combined LES and FW-H-AA approach. Some factors influencing on noise attenuation, such as the gasflow velocity, temperature and the structural parameters of the muffler are analyzed. The results show that the aerodynamic noise and turbulent kinetic energy (TKE) are mainly attributed to the structural mutations in the muffler. The outlet sound pressure level (SPL) increases with the inlet gasflow velocity and decreases with temperature. According to the factor analysis results, the target muffler is modified by adding a fillet transition to the end of inserted tube and redesigning the structures where the TKE concentrated for improving the aerodynamic performance. In terms of the outlet SPL, the inner TKE and the backpressure of the muffler, the modified muffler is significantly improved by the maximum reductions of 3-5dB in SPL, 10–20% in TKE and 0.5–2.5 kPa in backpressure. The presented method might be extended to other kinds of muffler for aeroacoustic calculation and improvement design.
8
Bozorgi, Alireza, Leonidas Siozos-Rousoulis, Seyyed Ahmad Nourbakhsh, and Ghader Ghorbaniasl. "A two-dimensional solution of the FW-H equation for rectilinear motion of sources." Journal of Sound and Vibration 388 (February 2017): 216–29. http://dx.doi.org/10.1016/j.jsv.2016.10.035.
Full text
9
Huang, Zhongjie, Leonidas Siozos-Rousoulis, Tim De Troyer, and Ghader Ghorbaniasl. "Helicopter rotor noise prediction using a convected FW-H equation in the frequency domain." Applied Acoustics 140 (November 2018): 122–31. http://dx.doi.org/10.1016/j.apacoust.2018.04.040.
Full text
10
Khelladi, Sofiane, and Farid Bakir. "A Consistency Test of Thickness and Loading Noise Codes Using Ffowcs Williams and Hawkings Equation." Advances in Acoustics and Vibration 2010 (July 4, 2010): 1–6. http://dx.doi.org/10.1155/2010/174361.
Full textAbstract:
The thickness noise predicted by the Ffowcs Williams and Hawkings (FW&H) equation depends on the normal velocity which is very sensitive to the meshing size. Isom showed that in far field a monopolar source is equivalent to a dipolar source induced by a uniform distribution of the load on the entire moving surface. The main objective of this paper is to determine a specific expression of Isom's thickness noise in time and frequency domains for subsonic fans. The scope of the proposed expression of Isom's thickness noise is to define a benchmark test of consistency for thickness and loading noise codes in both time and frequency domains for subsonic fans when using the free field solution of FW&H's equation.
11
Wang, Zeyang, Jun Huang, and Mingxu Yi. "Acoustic scattering effect prediction of helicopter fuselage based on BEM and convective FW–H equation." Acta Acustica 6 (2022): 24. http://dx.doi.org/10.1051/aacus/2022019.
Full textAbstract:
The main acoustic noise source of helicopters is supposed to be the rotor blades, but the scattering effect of the helicopter fuselage sometimes cannot be ignored. For the accuracy of acoustic noise prediction and the research on the scattering affections of the helicopter fuselage, an FWH–BEM Method (FBM) based on convective FW–H equation and boundary element method (BEM) is presented for the prediction of the noise scattering effects of helicopter fuselage and the approach to the calculation of a helicopter’s acoustic noise field. In this paper, different fuselage models are adopted for the comparisons of the acoustic noise scattered by different types of fuselages. According to the discovery that helicopter fuselages with sharp edges can bring more significant acoustic scattering effects, a research on the influence of radius of curvature (RC), which reflects the sharpness of fuselage sharp edges, is also carried out. In addition, the acoustic scattering effects of the same type of fuselage but with different length, width and height ratios are also compared for discovering the influences of the fuselage size. The presented FBM is efficient to analyze the acoustic scattering effects of the helicopter fuselage and predict the acoustic noise field, taking both the rotor and the fuselage into account. Besides, the research in this paper leads to the discovery of the influence factors of the acoustic scattering effects and helps the proper selection of the fuselage in a helicopter stealth design.
12
Ryu, Seo Yoon, Cheolung Cheong, Jong Wook Kim, and Byung il Park. "Development of virtual fan flow and acoustic performance testers based on RANS solvers and acoustic analogy." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 2 (August 1, 2021): 4336–42. http://dx.doi.org/10.3397/in-2021-2667.
Full textAbstract:
As the potential of computational resources dramatically increases, the so-called computer-aided engineering readily replaces experiment-based engineering in related industrial fields. In this study, the virtual fan flow and acoustic performance testers are developed using the RANS solvers and the acoustic analogy. Two types of forward-curved centrifugal fans are selected for numerical and experimental investigations into its flow and acoustic performances. First, to experimentally evaluate the performances of the centrifugal fan units, their P-Q curves and sound power levels are measured using a fan flow performance tester and a semi-anechoic chamber, respectively. Second, the virtual fan flow and acoustic performance testers are constructed using the RANS solvers and the acoustic analogy based on the FW-H equation and CFD method. The validity of the current virtual methods is confirmed by comparing the prediction results with the measured ones. During the validation, the effects of the wall functions, y+ distribution, and turbulence models on predicted flow performance accuracy are closely examined. The effects of the integral surfaces used for the computation of the FW-H equations are also assessed on the predicted spectral levels of sound pressure.
13
Zhou, Zhiteng, Yi Liu, Hongping Wang, and Shizhao Wang. "Mass-Conserved Solution to the Ffowcs-Williams and Hawkings Equation for Compact Source Regions." Aerospace 10, no. 2 (February 6, 2023): 148. http://dx.doi.org/10.3390/aerospace10020148.
Full textAbstract:
A mass-conserved formulation for the Ffowcs-Williams–Hawkings (FW–H) integral is proposed to suppress contributions of spurious mass flux to the far-field sound at very low Mach numbers. The far-field condition and compact-source region assumptions are employed. By using higher-order derivatives of Green’s function, an expansion of the integrand in the monopole term is performed. This expansion transforms the mass-flux like monopole term into a series including different orders of velocity moment. At very low Mach numbers, the zero-order term is exactly the contribution from the spurious mass flux. The proposed mass-conserved formulation is confirmed by using an unsteady dipole, a two-dimensional (2D) incompressible convecting vortex, a circular-cylinder flow, and a co-rotating vortex pair. Additional spurious mass flux is added to the unsteady dipole, 2D incompressible convecting vortex, and flows over a circular cylinder; and the spurious mass flux of the co-rotating vortex pair comes from the residual of an incompressible-flow simulation. The far-field sound is found to be sensitive to spurious mass flux in the unsteady dipole and 2D incompressible convecting vortex cases. Then, the computation of the monopole-term expansion with the flow over a circular cylinder is presented. Fast convergence performance was observed, suggesting that the expansion requires little extra computational resources. Finally, FW–H boundary dependence is observed in the co-rotating vortex-pair case and eliminated by using the proposed mass-conserved formulation.
14
Qiaorui, Si, Jinfeng Liu, Asad Ali, Zhongkun Jin, Mengfei Chen, Xu Hong, and Shahzad Iqbal. "Study on flow-induced noise propagation mechanism of cylinder–airfoil interference model by using large eddy simulation combined with vortex–acoustic equation." AIP Advances 13, no. 3 (March 1, 2023): 035305. http://dx.doi.org/10.1063/5.0138084.
Full textAbstract:
An innovative numerical prediction method of flow-induced noise is implemented to overcome the defect that the traditional acoustic analogy method cannot reflect the interaction between turbulence vortex and sound. The classical cylindrical–airfoil interference model is used to perform the simulation and compared with the experimental results. To start with the derivation of Powell’s vortex sound equation, an implicit three-dimensional model of the fluid–acoustic coupling field is established to process the unsteady iterative calculation. The large eddy simulation method is adopted to solve the unsteady flow, and the acoustic information is then calculated using the vortex acoustic equation at each iteration step. The vortex structures around the cylinder airfoil are identified and captured by the Q-criterion for further analysis of vortex–noise correlation mechanism. The flow-induced noise prediction results are finally compared with Ffowcs Williams–Hawkings (FW–H) acoustic analogy approach. The results show that the vortex shedding from the cylinder and the interaction between vortex shedding and airfoil have the greatest influence on the acoustic, and the far-field noise of the cylinder airfoil shows a partial “eight” dipole distribution. The calculated results of the vortex sound theory are closer to the experimental ones than the FW–H method. The research helps understand the vortex acoustic coupling mechanism of the cylinder–airfoil model and provides a more accurate numerical prediction of flow-induced noise.
15
Jia, S. H., B. Yang, X. L. Zhao, and J. Z. Xu. "Numerical simulation of far field acoustics of an airfoil using vortex method and 2-D FW-H equation." IOP Conference Series: Materials Science and Engineering 52, no. 2 (December 20, 2013): 022047. http://dx.doi.org/10.1088/1757-899x/52/2/022047.
Full text
16
Malainine, Maymouna, Amany Khaled, and Sameh M. Shabaan. "Aeroacoustics behavioral study of Savonius wind turbine." Journal of Physics: Conference Series 2128, no. 1 (December 1, 2021): 012033. http://dx.doi.org/10.1088/1742-6596/2128/1/012033.
Full textAbstract:
Abstract Vertical Axis Wind Turbines (VAWTs) are appropriate for use in populated areas. If VAWTs were installed at residential areas, the generated aerodynamic noise can be harmful in a way or another. Therefore, in the present study, the aero-acoustics of the conventional Savonius Wind turbine was investigated using Computational Fluid Dynamics (CFD). Both the Unsteady Reynolds-averaged Navier-Stokes (URANS) equations and impermeable Ffowcs Wiliams and Hawkings (FW-H) equation were simultaneously solved. The effect of speed ratio was also studied. The results indicate that; the pressure is inversely proportional to the speed ratio. Additionally, the velocity has been increased due to the increase of the tip speed ratio. Finally, it has improved that for the majority of receivers, the overall sound level increases with increasing speed ratio.
17
Qin, Qikai, Dejiang Shang, Yongwei Liu, and Tianyu Wang. "Prediction of flow noise around a cylinder based on Large-Eddy Simulation and acoustic analogy method." MATEC Web of Conferences 283 (2019): 08003. http://dx.doi.org/10.1051/matecconf/201928308003.
Full textAbstract:
In this article, a hybrid method combining large eddy simulation with acoustic analogy is presented to predict three-dimensional far field noise induced by flow around a cylinder. Firstly, the governing equation including RANS equations with shear-stress transport (SST) k-ω turbulent model is numerically solved for steady flow field by using Ansys Fluent. Transient flow field is numerically solved by LES. Then, the flow field simulation results are used to compute the flow-induced noise with the FW-H integral equation method and BEM method based on Lighthill acoustic analogy equation in Actran. Before using for flow around a cylinder, accuracy of flow turbulent model in predicting turbulent flow around a cylinder is tested by comparing with available experimental data. According on the simulation result, the characteristic of the acoustic field, noise at some special points in frequency domain, the noise radiation directivity are studied. Analysis of noise distribution and frequency spectrum curves shows that dipole source takes the dominant place in the noise around a cylinder under the conditions of this article. The flow noise around a cylinder is mainly concentrated in the low frequency range.
18
Diémé, Mohamad M., Maxime Hervy, Saïdou N. Diop, Claire Gérente, Audrey Villot, Yves Andres, and Courfia K. Diawara. "Sustainable Conversion of Agriculture and Food Waste into Activated Carbons Devoted to Fluoride Removal from Drinking Water in Senegal." International Journal of Chemistry 8, no. 1 (November 25, 2015): 8. http://dx.doi.org/10.5539/ijc.v8n1p8.
Full textAbstract:
<p>The objective of this study was to investigate the production of activated carbons (AC) from cashew shells, and millet stalks and their efficiency in fluoride retention. These agricultural residues are collected from Senegal. It is known that some regions of Sénégal, commonly called the groundnut basin, are affected by a public health problem caused by an excess of fluoride in drinking water used by these populations. The activated carbons were produced by a combined pyrolysis and activation with water steam; no other chemical compounds were added. Then, activated carbonaceous materials obtained from cashew shells and millet stalks were called CS-H<sub>2</sub>O and MS-H<sub>2</sub>O respectively. CS-H<sub>2</sub>O and MS-H<sub>2</sub>O show very good adsorbent features, and present carbon content ranges between 71 % and 86 %. The BET surface areas are 942 m² g<sup>-1</sup> and 1234 m².g<sup>-1</sup> for CS-H<sub>2</sub>O and MS-H<sub>2</sub>O respectively. A third activated carbon produced from food wastes and coagulation-flocculation sludge (FW/CFS-H<sub>2</sub>O) was produced in the same conditions. Carbon and calcium content of FW/CFS-H<sub>2</sub>O are 32.6 and 39.3 % respectively. The kinetics sorption were performed with all these activated carbons, then the pseudo-first equation was used to describe the kinetics sorption. Fluoride adsorption isotherms were performed with synthetic and natural water with the best activated carbon from kinetics sorption, Langmuir and Freundlich models were used to describe the experimental data. The results showed that carbonaceous materials obtained from CS-H<sub>2</sub>O and MS-H<sub>2</sub>O were weakly efficient for fluoride removal. With FW/CFS-H<sub>2</sub>O, the adsorption capacity is 28.48 mg.g<sup>-1 </sup>with r² = 0.99 with synthetic water.</p>
19
Hu, H. R., C. Zhang, and X. Wang. "Numerical acoustic simulation of flow around circular cylinders based on Lattice Boltzmann method and Ffowcs Williams-Hawkings acoustic equation." International Journal of Computational Materials Science and Engineering 07, no. 01n02 (June 2018): 1850010. http://dx.doi.org/10.1142/s2047684118500100.
Full textAbstract:
Based on the GPU acceleration technique, Lattice Boltzmann method (LBM) and Ffowcs Williams-Hawkings (FW-H) acoustic equation are adopted to simulate the noise generated by flow around fixed and rotating circular cylinders when Reynolds number (Re) is 200. The results show that the sound pressure level has a peak in the vertical direction and it is higher than that in the streamwise direction. The maximum sound pressure level is significantly reduced when the cylinder rotates due to the suppression of vortex shedding compared to the case of a fixed cylinder. For tandem cylinders, the maximum sound pressure level in the vertical direction increases as the spacing ratio increases, and for parallel cylinders, it decreases as the spacing ratio increases. In addition, when using graphic processing unit (GPU), the computational efficiency is improved greatly and the speed-up reaches nearly 100.
20
Hajczak, Antoine, Laurent Sanders, François Vuillot, and Philippe Druault. "A comparison between off and on-body control surfaces for the FW-H equation: Application to a non-compact landing gear wheel." Journal of Sound and Vibration 490 (January 2021): 115730. http://dx.doi.org/10.1016/j.jsv.2020.115730.
Full text
21
Long, Shuang Li, Hong Nie, and Xin Xu. "Aeroacoustic Study on a Simplified Nose Landing Gear." Applied Mechanics and Materials 184-185 (June 2012): 18–23. http://dx.doi.org/10.4028/www.scientific.net/amm.184-185.18.
Full textAbstract:
Simulation analysis and experiment research are performed on the aeroacoustic noise of a landing gear component in this paper. Detached Eddy Simulation (DES) is used to produce the flow field of the model. The Ffowcs-Williams/Hawkings (FW-H) equation is used to calculate the acoustic field. The sound field radiated from the model is measured in the acoustic wind tunnel. A comparison shows that the simulation results agree well with the experiment results under the acoustic far field condition. The results show that the noise radiated from the model is broadband noise. The directivity of the noise source is like a type of dipole. The wheel is the largest contributor and the strut is the least contributor to the landing gear noise. The results can provide some reference for low noise landing gear design.
22
Nitzsche, F., and D. G. Opoku. "Acoustic validation of a new code using particle wake aerodynamics and geometrically-exact beam structural dynamics." Aeronautical Journal 109, no. 1096 (June 2005): 257–67. http://dx.doi.org/10.1017/s0001924000000713.
Full textAbstract:
Abstract This paper describes the validation of a new code for prediction both aeroacoustic and aeroelastic behaviour of hingeless rotors. The structural component is based on a non-linear beam element model considering small strains and finite rotations, which uses a mixed variational intrinsic formulation. The aerodynamic component is built on a loworder panel method incorporating a vortex particle free-wake model. The aerodynamic and structural components are combined to form a closely coupled aeroelastic code that solves in the time-domain. The loading and thickness noise terms for the aeroacoustic calculations are calculated from the aerodynamic data using a formulation based on the Ffowcs Williams-Hawkings (FW-H) equation. The code is successfully validated for acoustic signature and BVI predictions using test cases from the HELINOISE program.
23
Le, Quang Quyen. "BUILDING AND VERIFYING A TOOL FOR CALCULATING THE AERODYNAMIC NOISE OF HELICOPTER ROTORS." Journal of Science and Technique 17, no. 5 (November 29, 2022): 58–69. http://dx.doi.org/10.56651/lqdtu.jst.v17.n05.530.
Full textAbstract:
This article presents an approach to build and verify a tool for calculating aerodynamic noise characteristics of helicopter rotors. The calculation tool is built on the basis of combining the vortex lattice method and the Formulation 1A of Farrasat, which is one of solutions of the Ffowcs Williams-Hawkings (FW-H) equation. By comparing the obtained result with data from reputable international publications, the calculation tool is verified for accuracy and reliability. The variation and value of the acoustic pressure from this calculation tool are in a good agreement with the international published works. Applying the tool in some specific calculation cases gives appropriate results, thereby giving important recommendations about the safe distance corresponding to the human hearing threshold for rotors with specific geometric dimensions and operating characteristics.
24
Souliez, F. J., L. N. Long, P. J. Morris, and A. Sharma. "Landing Gear Aerodynamic Noise Prediction Using Unstructured Grids." International Journal of Aeroacoustics 1, no. 2 (August 2002): 115–35. http://dx.doi.org/10.1260/147547202760236932.
Full textAbstract:
Aerodynamic noise from a landing gear in a uniform flow is computed using the Ffowcs Williams-Hawkings (FW-H) equation. The time accurate flow data on the integration surface is obtained using a finite volume low-order flow solver on an unstructured grid. The Ffowcs Williams-Hawkings equation is solved using surface integrals over the landing gear surface and over a permeable surface away from the landing gear. Two geometric configurations are tested in order to assess the impact of two lateral struts on the sound level and directivity in the far-field. Predictions from the Ffowcs Williams-Hawkings code are compared with direct calculations by the flow solver at several observer locations inside the computational domain. The permeable Ffowcs Williams-Hawkings surface predictions match those of the flow solver in the near-field. Far-field noise calculations coincide for both integration surfaces. The increase in drag observed between the two landing gear configurations is reflected in the sound pressure level and directivity mainly in the streamwise direction.
25
Chew, Ying Ming, and V. An-Erl King. "Microwave Drying of Pitaya (Hylocereus) Peel and the Effects Compared with Hot-Air and Freeze-drying." Transactions of the ASABE 62, no. 4 (2019): 919–28. http://dx.doi.org/10.13031/trans.13193.
Full textAbstract:
Abstract. Microwave drying (MD) of pitaya peel was performed at 75, 225, 375, 525, and 750 W. The drying effects on the effective moisture diffusivity (De), total polyphenol content (TPC), betalain content, DPPH scavenging ability, and rehydration abilities of pitaya peel were examined. The data were compared with hot-air drying (HD) at 100°C for 4 h and freeze-drying (FD) for 24 h. The results showed that the MD kinetics of pitaya peel fit Fick’s law and the Arrhenius equation with an activation energy (Ea) of 34.08 W g-1. The De values of MD, which ranged from 2.35E-07 m2 s-1 (at 75 W) to 5.56E-06 m2 s-1 (at 750 W), indicated that the effectiveness of MD was appreciably higher than that of HD (2.44E-08 m2 s-1) and FD (4.43E-09 m2 s-1). Although MD resulted in decreased betacyanin (9.31 mg L-1 extract) and betaxanthin (6.58 mg L-1 extract) contents, the DPPH inhibition of pitaya peel remained at 75% due to an increase in TPC (115 mg GAE per 100 FW). MD of pitaya peel can also provide higher rehydration ability than HD and was comparable to FD. This study concludes that MD of pitaya peel was highly effective while maintaining high levels of TPC and DPPH inhibition. Keywords: Arrhenius equation, Effective moisture diffusivity, Fick’s law, Microwave drying, Pitaya peel.
26
Shi, Fangcheng, Fushan Shi, Xudong Tian, and Tiantian Wang. "Numerical Study on Aerodynamic Noise Reduction of Pantograph." Applied Sciences 12, no. 21 (October 22, 2022): 10720. http://dx.doi.org/10.3390/app122110720.
Full textAbstract:
A hybrid method incorporating the simulations of noise sources with delayed detached eddy simulation (DDES) and calculations of far-field noise with the Ffowcs Williams–Hawkings (FW-H) equation is used to study the suppression technique for the aerodynamic noise of a Faiveley CX-PG pantograph. Considering that China’s Fuxing bullet trains operate at 350 km/h, the inflow velocity of 350 km/h is applied in this paper. The noise radiated from the panhead area, middle area, and bottom area at an inflow velocity of 350 km/h is distinguished. The noise intensities at the standard observer show that the noise radiated from the panhead area is the strongest, and the sound pressure level spectrum value is larger than the other two in the range above 500 Hz. The influence of applying the wavy rods and modifying the contact strip shape on the aerodynamic noise is discussed in detail. By comparing the acoustic source distribution and the far-field noise intensity, it is found that applying the wavy rods can effectively reduce the panhead noise, especially around the peak frequency. Modifying the shape of the contact strip to a hexagon can suppress the vortex shedding, leading to a lower surface pressure level. Combining the strip modification and wavy rods, the total noise intensity can be diminished by about 3.0 dB.
27
Ju, Shengjun, Zhenxu Sun, Dilong Guo, Guowei Yang, Yeteng Wang, and Chang Yan. "Aerodynamic-Aeroacoustic Optimization of a Baseline Wing and Flap Configuration." Applied Sciences 12, no. 3 (January 20, 2022): 1063. http://dx.doi.org/10.3390/app12031063.
Full textAbstract:
Optimization design was widely used in the high-lift device design process, and the aeroacoustic reduction characteristic is an important objective of the optimization. The aerodynamic and aeroacoustic study on the baseline wing and flap configuration was performed numerically. In the current study, the three-dimensional Large Eddy Simulation (LES) equations coupled with dynamic Smagorinsky subgrid model and Ffowcs–William and Hawkings (FW–H) equation are employed to simulate the flow fields and carry out acoustic analogy. The numerical results show reasonable agreement with the experimental data. Further, the particle swarm optimization algorithm coupled with the Kriging surrogate model was employed to determine optimum location of the flap deposition. The Latin hypercube method is used for the generation of initial samples for optimization. In addition, the relationship between the design variables and the objective functions are obtained using the optimization sample points. The optimized maximum overall sound pressure level (OASPL) of far-field noise decreases by 3.99 dB with a loss of lift-drag ratio (L/D) of less than 1%. Meanwhile, the optimized performances are in good and reasonable agreement with the numerical predictions. The findings provide suggestions for the low-noise and high-lift configuration design and application in high-lift devices.
28
Li, Long Shuang, Hong Nie, and Xin Xu. "Simulation and Experiment on Landing Gear Component Noise." Applied Mechanics and Materials 170-173 (May 2012): 3454–59. http://dx.doi.org/10.4028/www.scientific.net/amm.170-173.3454.
Full textAbstract:
Simulation analysis and experiment research are performed on the aeroacoustic noise of a landing gear component in this paper. Detached Eddy Simulation (DES) is used to produce the flow field of the model. The Ffowcs-Williams/Hawkings (FW-H) equation is used to calculate the acoustic field. The sound field radiated from the model is measured in the acoustic wind tunnel. A comparison shows that the simulation results agree well with the experiment results under the acoustic far field condition. The results show that the noise radiated from the model is broadband noise. The directivity of the noise source is like a type of dipole. The location between shock absorber and strut, shock absorber and bogie can induce the interaction noise which is presented by two energy peaks in the spectra. The shock absorber and the bogie is the main contributor while the strut is the least contributor to the total noise.
29
Gu, Mengfan, and Baowei Song. "Aeroacoustic Noise Characteristics of Flow around a Square Column Based on Large Eddy Simulation." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 38, no. 3 (June 2020): 465–70. http://dx.doi.org/10.1051/jnwpu/20203830465.
Full textAbstract:
Large eddy simulation and Ffowcs Williams-Hawkings (FW-H) equation were used to investigate the aeroacoustic noise characteristics of flow around a square column. After verifying the accuracy of the numerical model, the influences of flow velocity and flow direction on noise field characteristics are discussed. The noise prediction result of the base model was in good agreement with the experiment data in the vortex-shedding frequency and in the general trend. It was shown that there were typical dipole noise sources in the direction of 110° and 250°, respectively. With the increase of distance, the total sound pressure level was decreased and the directionality of the noise field is becoming worse. The results showed that the vortex-shedding frequency was increased with the increase of flow velocity, and the corresponding sound pressure level was also raised. The change of flow direction would make the directionality of noise flied more complicated, which is related to the complexity of flow field.
30
Yu, An, Xincheng Wang, Zhipeng Zou, Qinghong Tang, Huixiang Chen, and Daqing Zhou. "Investigation of Cavitation Noise in Cavitating Flows around an NACA0015 Hydrofoil." Applied Sciences 9, no. 18 (September 7, 2019): 3736. http://dx.doi.org/10.3390/app9183736.
Full textAbstract:
To provide theoretical basis for cavitation noise control, the cavitation evolution around a hydrofoil and its induced noise were numerically investigated. A modified turbulence model and Zwart cavitation model were employed to calculate the flow field and predict the cavitation phenomenon accurately. Then, the acoustic analogy method based on the Ffowcs Williams-Hawking (FW-H) equation was applied to analyze the cavitation-induced noise. Seven cavitation numbers were selected for analysis. Acoustic power spectral density (PSD) and acoustic pressure were investigated to establish the relationship between cavitation number and their acoustic characteristics. It was indicated that as cavitation number decreases, cavitation cycle length gets shorter and the magnitude of acoustic power spectral density increases dramatically. One peak value of acoustic power spectral density induced by the extending and retracting of leading-edge cavitation can be obtained under sheet cavitation conditions, while under cloud cavitation, two peak values of acoustic power spectral density can be obtained and are induced by superposition from leading-edge cavitation and trailing vortex.
31
Nose, H., G. W. Mack, X. R. Shi, and E. R. Nadel. "Shift in body fluid compartments after dehydration in humans." Journal of Applied Physiology 65, no. 1 (July 1, 1988): 318–24. http://dx.doi.org/10.1152/jappl.1988.65.1.318.
Full textAbstract:
To investigate the influence of [Na+] in sweat on the distribution of body water during dehydration, we studied 10 volunteer subjects who exercised (40% of maximal aerobic power) in the heat [36 degrees C, less than 30% relative humidity (rh)] for 90-110 min to produce a dehydration of 2.3% body wt (delta TW). After dehydration, the subjects rested for 1 h in a thermoneutral environment (28 degrees C, less than 30% rh), after which time the changes in the body fluid compartments were assessed. We measured plasma volume, plasma osmolality, and [Na+], [K+], and [Cl-] in plasma, together with sweat and urine volumes and their ionic concentrations before and after dehydration. The change in the extracellular fluid space (delta ECF) was estimated from chloride distribution and the change in the intracellular fluid space (delta ICF) was calculated by subtracting delta ECF from delta TW. The decrease in the ICF space was correlated with the increase in plasma osmolality (r = -0.74, P less than 0.02). The increase in plasma osmolality was a function of the loss of free water (delta FW), estimated from the equation delta FW = delta TW - (loss of osmotically active substance in sweat and urine)/(control plasma osmolality) (r = -0.79, P less than 0.01). Free water loss, which is analogous to "free water clearance" in renal function, showed a strongly inverse correlation with [Na+] in sweat (r = -0.97, P less than 0.001). Fluid movement out of the ICF space attenuated the decrease in the ECF space.(ABSTRACT TRUNCATED AT 250 WORDS)
32
Malefaki, Iro, and Kostas Belibassakis. "A Novel FDTD–PML Scheme for Noise Propagation Generated by Biomimetic Flapping Thrusters in the Ocean Environment." Journal of Marine Science and Engineering 10, no. 9 (September 3, 2022): 1240. http://dx.doi.org/10.3390/jmse10091240.
Full textAbstract:
Biomimetic flapping-foil thrusters can operate efficiently while offering desirable levels of thrust required for the propulsion of a small vessel or an Autonomous Underwater Vehicle (AUV). These systems have been studied both as main propulsion devices and for augmenting ship propulsion in waves. In this work, the unsteady hydrofoil loads are used to calculate the source terms of the Ffowcs Williams–Hawkings (FW-H) equation which is applied to model noise propagation in the underwater ocean acoustic environment. The solution provided by a simplified version of the Farassat formulation in free space is extended to account for a bounded domain and an inhomogeneous medium, characterizing the sea acoustic waveguide. Assuming the simplicity azimuthal symmetry of the environmental parameters, a numerical model is developed based on a Finite Difference Time Domain (FDTD) scheme, incorporating free-surface and seabed effects, in the presence of a variable sound speed profile. For the treatment of the outgoing radiating field, a Perfectly Matched Layer (PML) technique is implemented. Numerical results are presented illustrating the applicability of the method.
33
Guo, Jing, Xiao-Ming Tan, Zhi-Gang Yang, Yu-Qi Xue, Ya-Nan Shen, and Hao-Wei Wang. "Aeroacoustic Optimization Design of the Middle and Upper Part of Pantograph." Applied Sciences 12, no. 17 (August 30, 2022): 8704. http://dx.doi.org/10.3390/app12178704.
Full textAbstract:
The pantograph is the main noise source of high-speed trains, of which the middle and upper parts of the pantograph account for about 50% of the whole noise energy. Taking CRH380BL pantograph as the basic prototype, three aerodynamic noise reduction measures of opening, slotting, and airfoil are introduced to build a new pantograph, and their aeroacoustic performances are comprehensively investigated through large eddy simulation (LES) and Ffowcs Williams–Hawkings (FW-H) equation method. The research results show that the open upper and lower arms (ULA) can reduce the downstream vorticity intensity and vortex structure scale, which in turn reduces the noise source intensity, thus reducing their radiated noise by approximately 1.1 dBA. The slotted ULA reduce the size of the rear vortex structure but increase the vorticity intensity, so it is difficult to effectively control their radiated noise. The airfoil bow head reduces the vorticity intensity and vortex structure scale behind it, and avoids periodic vortex shedding, thereby reducing its noise source intensity, thus reducing its radiated noise by about 1.2 dBA.
34
Rismondo, Giacomo, Marta Cianferra, and Vincenzo Armenio. "Acoustic Response of a Vibrating Elongated Cylinder in a Hydrodynamic Turbulent Flow." Journal of Marine Science and Engineering 10, no. 12 (December 6, 2022): 1918. http://dx.doi.org/10.3390/jmse10121918.
Full textAbstract:
The present paper contains the results of the numerical analysis of the interaction between a Newtonian incompressible turbulent flow and a linear elastic slender body, together with the influence of the fluid–structure interaction (FSI) on the noise generation and propagation. The purpose is to evaluate the differences in term of acoustic pressure between the case where the solid body is rigid (infinite stiffness) and the case where it is elastic (finite stiffness). A partitioned and implicit algorithm with the arbitrary Lagrangian–Eulerian method (ALE) is used for the interaction between the fluid and solid. For the evaluation of the turbulent fluid motion, we use a large eddy simulation (LES) with the Smagorinsky subgrid scale model. The equation for the solid is solved through the Lagrangian description of the momentum equation and the second Piola–Kirchoff stress tensor. In addition, the acoustic analogy of Lighthill is used to characterize the acoustic source (the slender body) by directly using the fluid dynamic fields. In particular, we use the Ffowcs Williams and Hawkings (FW-H) equation for the evaluation of the acoustic pressure in the fluid medium. As a first numerical experiment, we analyze a square cylinder immersed in a turbulent flow characterized by two different values of stiffness: one infinite (rigid case) and one finite (elastic case). In the latter case, the body stiffness and mean flow velocity are such that they induce the lock-in phenomenon. Finally, we evaluate the differences in terms of acoustic pressure between the two different cases.
35
Purwana, Agung, I. Made Ariana, and Wisnu Wardhana. "Numerical study on the cavitation noise of marine skew propellers." Journal of Naval Architecture and Marine Engineering 18, no. 2 (December 31, 2021): 97–107. http://dx.doi.org/10.3329/jname.v18i2.38099.
Full textAbstract:
In this study, numerical simulations on the noise of the underwater marine propeller for different pressures, skew angles, and performance conditions are investigated. The study has been carried out for the prediction of cavity and noise cavitation characteristics of the propeller. The blade sheet cavitation created by an underwater propeller is then evaluated using numerical analysis. The cavitation and cavity around marine propellers were predicted using MRF (Multiple Reference Frame) techniques. The simulation uses the Reynolds Averaged Navier-Stokes (RANS) formulation with the turbulence model k-ω Shear Stress Transport and the Fast Fourier Transform. The FW-H equation is used to measure far-field radiation under various operating conditions. The simulation is carried out to present that the pressure and skew propeller angles have an effect on the form and area of the cavity, as well as cavitation noise. The noise characteristics at various positions of hydrophones and speeds of the marine propeller are presented. The 3D model of B-series marine propeller with D=250 mm, Z=4, P/D= 1.0, AE/AO=0.55, skew angles of 16, 35, 53, and 72 degrees at advance coefficient, J=0.221, is used for the simulation
36
Song, Xiang, Peixun Yu, Junqiang Bai, Xiao Han, and Jiahui Peng. "Aerodynamic and Aeroacoustic Optimization of Propeller Based on Hanson Noise Model." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 38, no. 4 (August 2020): 685–94. http://dx.doi.org/10.1051/jnwpu/20203840685.
Full textAbstract:
Aiming at the multi-objective optimization design problem of propeller aerodynamics and noise, the three-dimensional geometric deformation of the whole blade is carried out by the free-form surface deformation method based on non-uniform rational B-spline. In order to save the calculation cost of optimization, the RANS method and the Hanson model are combined to predict pure tone noise, and the prediction accuracy is comparable to the accuracy of the FW-H equation coupled with URANS method. Kriging surrogate model and non-dominated sorting genetic algorithm are used to search for optimal value, and a multi-objective optimization design framework for propeller aerodynamics and noise is established. This method is used to optimize the blade shape of a passenger airliner propeller, and the airfoil torsion angle and chord length of different positions are optimized as design variables. Compared with the basic blade, the noise value of the axial monitoring point near the cruise configuration under the wind tunnel experiment condition is reduced by about 0.25 dB at the same time as the power is reduced. In the case of a slight increase in power, the noise is reduced by about 1 dB.
37
Belibassakis, Kostas, John Prospathopoulos, and Iro Malefaki. "Scattering and Directionality Effects of Noise Generation from Flapping Thrusters Used for Propulsion of Small Ocean Vehicles." Journal of Marine Science and Engineering 10, no. 8 (August 17, 2022): 1129. http://dx.doi.org/10.3390/jmse10081129.
Full textAbstract:
Flapping-foil thrusters are systems that operate at a substantially lower frequency compared with marine propellers and are characterized by a much smaller power concentration. These biomimetic devices are able to operate very efficiently, offering desirable levels of thrust required for the propulsion of small vessels or autonomous underwater vehicles (AUVs), and can be used for the standalone propulsion of small vessels or for augmenting ship propulsion in waves, alleviating the generation of noise and its adverse effects on sea life, particularly on marine mammals. In this work, we consider the generation of noise by flapping foils arranged in the neighborhood of the above vessels including the scattering effects by the hull, which, in addition to free-surface and seabed effects, significantly contribute to the modification of the characteristics of the acoustic field. A Boundary Element Method (BEM) is developed to treat the 3D scattering problem in the frequency domain forced by monopole and dipole source terms associated with the Ffowcs Williams and Hawkings (FW-H) equation. Numerical results are presented in selected cases illustrating that the hull geometry and acoustic properties, as well as the sea surface and seabed effects, are important for the determination of the directionality of the generated noise and significantly affect the propagation in the underwater ocean environment.
38
Li, Fang, Qiaogao Huang, Guang Pan, and Yao Shi. "Effect of wavy leading edge on hydrofoil-turbulence interaction noise." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 39, no. 6 (December 2021): 1266–73. http://dx.doi.org/10.1051/jnwpu/20213961266.
Full textAbstract:
In order to solve the underwater noise pollution and improve the acoustic stealth performance of underwater vehicles, NACA0020 was bionically modified according to the structure of the leading edge tubercles of humpback fin. The flow field and noise characteristics of the hydrofoil-turbulent interaction model before and after the modification were studied by using the large eddy simulation and the FW-H equation. The results show that the wavy leading edge can effectively reduce the turbulence interaction noise of the hydrofoil, especially the broadband noise after 89.55 Hz. The overall sound pressure level(OASPL) directivity of the wavy leading edge hydrofoil are the same as the original hydrofoil, and both have dipole characteristics, but the noise value in all directions is reduced to a certain extent. The OASPL is calculated and analyzed in different frequency bands. The results show that the OASPL has a best reduction in 1 000-5 000 Hz frequency band, and the noise can be reduced up to 12.6 dB. Through the analysis of flow field, it is concluded that the noise reduction effect of wavy leading edge mainly relates to the decrease in pressure fluctuation at leading edge and the decrease in coherence of vortex in spanwise direction caused by the enhancement of spanwise flow.
39
Dang, Zhigao, Zhaoyong Mao, and Wenlong Tian. "Reduction of Hydrodynamic Noise of 3D Hydrofoil with Spanwise Microgrooved Surfaces Inspired by Sharkskin." Journal of Marine Science and Engineering 7, no. 5 (May 10, 2019): 136. http://dx.doi.org/10.3390/jmse7050136.
Full textAbstract:
Loud hydrodynamic noise is not only potentially harmful to the health of organisms in the ocean, but it is also a threat to the survival of underwater vehicles. Different from the general noise reduction technologies at present, a new idea for a flow-induced noise reduction design with spanwise microgrooved surfaces inspired by sharkskin is introduced in this paper. Large eddy simulations (LES) combined with the Ffowcs Williams and Hawkings (FW-H) equation are adopted to simulate the hydrodynamic noise of the three-dimensional (3D) hydrofoil. The accuracy of the numerical predictions is checked against existing experimental data, achieving good agreement. With the increase of observing distance, the noise reduction effect at the trailing edge direction is gradually apparent, and a maximum noise reduction of up to 7.28 dB can be observed. It is seen from the noise spectra of the biomimetic hydrofoil that the main peaks are eliminated, and the noise level at high frequency is also decreased. The cause of noise reduction lies in the secondary vortex generated in the microgrooves, which hinder the process of turbulence, consume the energy of the flow, and weaken the intensity of turbulent burst. The results of this study provide a new way to design low-noise underwater structures with hydrofoils.
40
Shi, Lei, Wen Qiang Wang, Cheng Chun Zhang, Jing Wang, and Lu Quan Ren. "The Effect of Bionic V-Ring Surface on the Aerodynamic Noise of a Circular Cylinder." Applied Mechanics and Materials 461 (November 2013): 751–62. http://dx.doi.org/10.4028/www.scientific.net/amm.461.751.
Full textAbstract:
Inspired by stripe shaped structure of owl wing feathers, V-ring surface was proposed in this paper to reduce the aerodynamic noise of a circular cylinder. The effects of V-ring surface on the aerodynamic and aeroacoustic performance of the cylinder were investigated by wind tunnel and numerical simulation. We tested the fluctuating pressure of the smooth cylinder and the V-ring surface cylinder by pulsating pressure sensor in FD-09 wind tunnel of China Academy of Aerospace Aerodynamics（CAAA）. At a wind speed of 42m/s, the Reynolds number is 1.62×105based on the cylinder diameter D of 58mm. The test results showed that the overall fluctuating pressure on the measurement points of the V-ring surface cylinder was significantly decreased compared with the smooth cylinder. The mechanisms of aerodynamic noise control of circular cylinder by V-ring surface were studied by the Large Eddy Simulation（LES）and the Ffowcs Williams and Hawkings （FW-H） equation. The numerical simulation results showed that the aerodynamic noise of the V-ring surface cylinder was reduced by 4.1dB compared to the smooth cylinder. The sound pressure of V-ring surface cylinder model is reduced when the lift fluctuation becomes lower. The V-ring surface is capable of reducing the frequency of the vortex shedding and controlling the fluctuating lift force induced by unstable vortices acting on the cylinder surface.
41
Liu, Xiaomin, and Xiang Liu. "A Numerical Study of Aerodynamic Performance and Noise of a Bionic Airfoil Based on Owl Wing." Advances in Mechanical Engineering 6 (January 1, 2014): 859308. http://dx.doi.org/10.1155/2014/859308.
Full textAbstract:
Noise reduction and efficiency enhancement are the two important directions in the development of the multiblade centrifugal fan. In this study, we attempt to develop a bionic airfoil based on the owl wing and investigate its aerodynamic performance and noise-reduction mechanism at the relatively low Reynolds number. Firstly, according to the geometric characteristics of the owl wing, a bionic airfoil is constructed as the object of study at Reynolds number of 12,300. Secondly, the large eddy simulation (LES) with the Smagorinsky model is adopted to numerically simulate the unsteady flow fields around the bionic airfoil and the standard NACA0006 airfoil. And then, the acoustic sources are extracted from the unsteady flow field data, and the Ffowcs Williams-Hawkings (FW-H) equation based on Lighthill's acoustic theory is solved to predict the propagation of these acoustic sources. The numerical results show that the lift-to-drag ratio of bionic airfoil is higher than that of the traditional NACA 0006 airfoil because of its deeply concave lower surface geometry. Finally, the sound field of the bionic airfoil is analyzed in detail. The distribution of the A-weighted sound pressure levels, the scaled directivity of the sound, and the distribution of dP/dt on the airfoil surface are provided so that the characteristics of the acoustic sources could be revealed.
42
Li, Zhengnong, and Jianan Li. "Numerical Simulation Study of Aerodynamic Noise in High-Rise Buildings." Applied Sciences 12, no. 19 (September 21, 2022): 9446. http://dx.doi.org/10.3390/app12199446.
Full textAbstract:
In order to study the aerodynamic noise on the surfaces of high-rise buildings under the action of strong winds, this paper numerically simulated the sound pressure field on the surface of a high-rise building using the large-eddy simulation method combined with the acoustic analog method of FW-H (Ffowcs Williams–Hawkings) equation and obtained the intensity radiation distribution of sound pressure on the surface of the building to further identify the area with the maximum sound pressure intensity of the noise radiation and thus achieve the purpose of locating noise source. The accuracy of the numerical simulation results for aerodynamic noise obtained in this paper was then verified by comparing with the acoustic wind tunnel experimental results. The locations of noise source obtained by numerical simulation and acoustic wind tunnel experiment were in good agreement. The sound pressure intensity pulsation time course was measured by the acoustic wind tunnel experiment, and the noise sound pressure level spectrum of each part of the building surface was obtained by fast Fourier transform (FFT). Furthermore, the spectral characteristics of the noise sound pressure level were analyzed. The results of the sound pressure level spectrum of aerodynamic noise obtained from the numerical simulation were compared with the acoustic wind tunnel experimental results, which were found to be very similar. The analysis of the sound pressure level spectrum of aerodynamic noise on the building surface reveals that the numerical simulation results in the middle- and high-frequency bands of the spectrum are in good agreement with the acoustic wind tunnel experimental results, but there is a difference between those in the low-frequency bands and the acoustic wind tunnel experimental results. The microphone array used to locate the noise source in the acoustic wind tunnel was found to suffer non-eliminable measurement errors, which might be a potential reason for a reasonably slight difference between the experimental and numerical simulation results. The background noise in the low-frequency band of the acoustic wind tunnel sound pressure level spectrum was relatively large, while there was basically no background noise in the numerical simulation. This paper shows that the numerical simulation method combined with large-eddy simulation and acoustic analogy (FW-H) can calculate the aerodynamic noise intensity at various points on the surfaces of high-rise buildings and reasonably predict the location of sound source. In addition, the numerical simulation results are similar to the acoustic wind tunnel experimental results in most frequency bands.
43
Su, Taoyong, Yang Lu, Jinchao Ma, and Shujun Guan. "Electrically Controlled Rotor Blade Vortex Interaction Airloads and Noise Analysis Using Viscous Vortex Particle Method." Shock and Vibration 2019 (November 6, 2019): 1–15. http://dx.doi.org/10.1155/2019/9678970.
Full textAbstract:
An electrically controlled rotor (ECR), also called a swashplateless rotor, replaces a swashplate with a trailing-edge flap system to implement primary rotor control. To investigate the aerodynamic characteristics of an ECR in blade-vortex interaction (BVI) condition, an analysis model based on the viscous vortex particle method, ECR blade pitch equation, and the Weissinger-L lifting surface model is established. In this model, the ECR wake flow field vorticity is discretized as multiple vortex particles, and the vorticity-velocity form of the Navier-Stokes equation is solved to simulate the transport diffusion of the vorticity. The flap motion-inducing blade-pitch movement is obtained by solving the ECR blade-pitch movement equation via the Runge–Kutta fourth-order method. On the basis, BVI noise radiation of an ECR is evaluated using the Ffowcs Williams and Hawkings (FW-H) equation. Based on the present prediction model, the aerodynamic and acoustic characteristics of a sample ECR in BVI condition are analyzed. The results show that since the BVI event of the ECR on the advancing side is mainly caused by the interaction between the flap tip vortex and the blade, the blade spanwise range of ECR BVI occurrence on the advancing side is smaller than that of the conventional rotor. In addition, the magnitude of the maximum sound pressure level on the advancing side as well as on the retreating side of the ECR is also different from that of the conventional rotor, which is consistent with the difference in the airloads between the ECR and conventional rotor. Furthermore, a study was performed to examine the effect of the pre-index angle on the BVI-induced airloads and noise. The amplitude of the impulsive airloads of the ECR on the advancing side is increased with the increase in pre-index angle, while the amplitude of the impulsive airloads of the ECR on the retreating side is decreased. Indeed, when the pre-index angle of the sample ECR is 8 degrees, the retreating-side noise radiation lobe is almost disappeared. In addition, the different intensity of wake vorticity is the main reason for the differences of the BVI-induced airloads and noise among the ECR with different pre-index angles.
44
Zhang, Cheng Chun, Wen Qiang Wang, Lei Shi, Jing Wang, and Lu Quan Ren. "Experimental and Numerical Study on Aerodynamic Noise Reduction of Cylindrical Rod with Bionic Wavy Surface." Applied Mechanics and Materials 461 (November 2013): 690–701. http://dx.doi.org/10.4028/www.scientific.net/amm.461.690.
Full textAbstract:
Inspired by the non-smooth structure of the leading edge of owls wing,a bionic wavy cylindrical surface is proposed in this paper to reduce the aerodynamic noise of a cylindrical rod. The effects of bionic wavy surface on the aerodynamic and aeroacoustic performance of the cylinder are investigated by wind tunnel and numerical simulation. The fluctuating pressure of the smooth cylinder and the bionic wavy surface cylinder are tested by pulsating pressure sensors in FD-09 low speed wind tunnel of China Aerospace Aerodynamics Research Institute. The fluctuating pressure of the bionic wavy surface cylinder is significantly lower than that of the smooth cylinder. We used the software ANSYS FLUENT to research the effect of the bionic wavy surface on the aerodynamic characteristics and aerodynamic noise of a cylinder by the Large Eddy Simulation (LES) and the Ffowcs Williams and Hawkings (FW-H) equation. Compared with the smooth cylinder, the aerodynamic noise of the bionic wavy cylinder is reduced by 6.7dB. A study of the relationship between the fluctuating lift and the aerodynamic noise size is conducted. We found that the sound pressure level of the wavy surface cylinder is significantly lower when the lift fluctuation amplitude decreased. Bionic wavy surface can effectively restrain the separated shear layer transition to turbulence. The frequency of vortex shedding which causes the lift fluctuations is reduced, so the aerodynamic noise of the circular cylinder is reduced. Keywords: bionics, cylindrical rod, wavy surface, aerodynamic noise, flow control
45
Wang, Zeyang, Jun Huang, Mingxu Yi, and Shaoze Lu. "A Dynamic RCS and Noise Prediction and Reduction Method of Coaxial Tilt-Rotor Aircraft Based on Phase Modulation." Sensors 22, no. 24 (December 11, 2022): 9711. http://dx.doi.org/10.3390/s22249711.
Full textAbstract:
For tilt-rotor aircraft with coaxial rotors (coaxial rotor aircraft), reduction of radar cross section as well as acoustic noise can be essential for stealth design, and the rotation of the coaxial rotors can have an influence on noise and dynamic radar cross section (RCS) characteristics. In this paper, an approach to the prediction of both the sound pressure level (SPL) of noise and the dynamic RCS of coaxial-tilt aircraft is carried out, based on the theories of the FW-H equation, the physics optics method (PO) and the physical theory of diffraction (PTD) method. In order to deal with the rotating parts (mainly including coaxial rotors), a generated rotation matrix (GRM) is raised, aiming at giving a universal formula for the time-domain grid coordinate transformation of all kinds of rotation parts with arbitrary rotation centers and rotation axis directions. Moreover, a compass-scissors model (CSM) reflecting the phase characteristics of coaxial rotors is established, and a method of noise reduction and RCS reduction based on the phase modulation method is put forward in this paper. The simulation results show that with proper CSM parameter combinations, the reduction of noise SPL can reach approximately 3~15 dB and the reduction of dynamic RCS can reach 1.6 dBsm at most. The dynamic RCS and noise prediction and reduction method can be meaningful for the radar-acoustic stealth design of coaxial tilt-rotor aircrafts.
46
Xu, Wei, and Feng Xu. "Numerical Study on Wind-Induced Noise of High-Rise Building Curtain Wall with Outside Shading Devices." Shock and Vibration 2018 (July 8, 2018): 1–12. http://dx.doi.org/10.1155/2018/5840761.
Full textAbstract:
Perforation metal plates with dense holes are often used as external curtain walls of high-rise buildings. When air flow passes through these holes at a high speed, complex vortex is generated and causes a significant issue of wind-induced noise. In this study, both Reynolds-averaged Navier–Stokes (RANS) simulations and large-eddy simulations (LES) were conducted to study flow around high-rise buildings with an external sunshade curtain wall. First, wind speed distributions at the height of a typical level under 16 wind directions were acquired. Then, the maximum wind speed ratio and its corresponding azimuth were identified. Second, the sound pressure levels in the vicinity of the shading devices with two types of perforation plate schemes were calculated to evaluate the acoustic characteristics by using the FW-H equation to simulate sound generation and propagation. The results indicate that the maximum wind speed around the buildings exists at the building corners, and the maximum wind speed ratio is 2.8 observed at 0-degree wind direction. Under two different wind conditions, the aeroacoustic performance of perforation plate is enhanced with reducing end plate size and increasing aperture size. The overall sound pressure level (OSPL) and A-weighted sound pressure level (ASPL) around the shading devices are 80 dB and 68 dB(A), respectively, for the improved perforation plate scheme under the 1-year return period maximum speed, which are changed to 58dB and 45dB(A) under the annual average speed. Therefore, it is believed that perforation plates with small end plate size and large aperture size are desirable for the noise prevention design of shading devices.
47
Yao, Hua-Dong, Zhongjie Huang, Lars Davidson, Jiqiang Niu, and Zheng-Wei Chen. "Blade-Tip Vortex Noise Mitigation Traded-Off against Aerodynamic Design for Propellers of Future Electric Aircraft." Aerospace 9, no. 12 (December 15, 2022): 825. http://dx.doi.org/10.3390/aerospace9120825.
Full textAbstract:
We study noise generation at the blade tips of propellers designed for future electric aircraft propulsion and, furthermore, analyze the interrelationship between noise mitigation and aerodynamics improvement in terms of propeller geometric designs. Classical propellers with three or six blades and a conceptual propeller with three joined dual-blades are compared to understand the effects of blade tip vortices on the noise generation and aerodynamics. The dual blade of the conceptual propeller is constructed by joining the tips of two sub-blades. These propellers are designed to operate under the same freestream flow conditions and similar electric power consumption. The Improved Delayed Detached Eddy Simulation (IDDES) is adopted for the flow simulation to identify high-resolution time-dependent noise sources around the blade tips. The acoustic computations use a time-domain method based on the convective Ffowcs Williams–Hawkings (FW-H) equation. The thrust of the 3-blade conceptual propeller is 4% larger than the 3-blade classical propeller and 8% more than the 6-blade one, given that they have similar efficiencies. Blade tip vortices are found emitting broadband noise. Since the classical and conceptual 3-blade propellers have different geometries, especially at the blade tips, they introduce deviations in the vortex development. However, the differences are small regarding the broadband noise generation. As compared to the 6-blade classical propeller, both 3-blade propellers produce much larger noise. The reason is that the increased number of blades leads to the reduced strength of tip vortices. The findings indicate that the noise mitigation through the modification of the blade design and number can be traded-off by the changed aerodynamic performance.
48
Li, Kewei, Taoyong Su, Yang Lu, and Qijun Zhao. "Nonharmonic Control of the Blade-Vortex Interaction Noise of Electrically Controlled Rotor." International Journal of Aerospace Engineering 2022 (September 9, 2022): 1–17. http://dx.doi.org/10.1155/2022/5353681.
Full textAbstract:
Electrically controlled rotor, also known as swashplateless rotor, represents an active rotor system that, due to the use of a trailing edge flap system instead of a swashplate, not only enables primary control but also conveniently reduces the blade-vortex interaction (BVI) noise of the rotors through active control. The effect of nonharmonic inputs on the control of the BVI noise of electrically controlled rotors based on their unique trailing edge flap systems has been investigated in this paper. To this end, an analytical model for the vortex interaction-induced load and noise of electrically controlled rotor is first established based on the viscous vortex particle method, the Weissinger-L blade model, and the Ffowcs Williams-Hawkings (FW-H) equation. On this basis, a simulation study of flap nonharmonic control for BVI noise reduction in electrically controlled rotors is carried out. According to the mechanism of the BVI in electrically controlled rotors, the second quadrant flap nonharmonic control is used to reduce the advancing side BVI noise, and the effects of different control waveforms and amplitudes on the peak value and directivity of the BVI noise of the sample electrically controlled rotors are analyzed to reveal the noise reduction mechanism of flap nonharmonic control. Subsequently, the effect of the third quadrant flap nonharmonic control on BVI noise on the retreating side of the sample electrically controlled rotors is investigated. The results show that flap nonharmonic control has little effect on miss distance and that it controls BVI noise mainly by reducing the wake vortex strength on the advancing and retreating sides, which may lead to an increase in rotor noise in other regions; the noise reduction effect of flap nonharmonic control for different blade preindex angles indicates that suitable preindex angles coupled with flap nonharmonic control help optimally reduce noise.
49
Ebrahimi, Abouzar, Mohammad Saeed Seif, and Ali Nouri-Borujerdi. "Noise Calculation of Non-cavitating Marine Propellers by Solving FW-H Acoustic Equations." مهندسی دریا 15, no. 30 (January 1, 2020): 13–22. http://dx.doi.org/10.29252/marineeng.15.30.13.
Full text
50
Ebrahimi, Abouzar, Mohammad Saeed Seif, and Ali Nouri-Borujerdi. "Hydrodynamic and Acoustic Performance Analysis of Marine Propellers by Combination of Panel Method and FW-H Equations." Mathematical and Computational Applications 24, no. 3 (September 9, 2019): 81. http://dx.doi.org/10.3390/mca24030081.
Full textAbstract:
The noise emitted by ships is one of the most important noises in the ocean, and the propeller noise is one of the major components of the ship noise. Measuring the propeller noise in a laboratory, despite the high accuracy and good reliability, has high costs and is very time-consuming. For this reason, the calculation of propeller noise using numerical methods has been considered in recent years. In this study, the noise of a propeller in non-cavitating conditions is calculated by the combination of the panel method (boundary element method) and solving the Ffowcs Williams-Hawkings (FW-H) equations. In this study, a panel method code is developed, and the results are validated by the experimental results of the model tests carried out in the cavitation tunnel of the Sharif University of Technology. Software for numerical calculation of propeller noise, based on FW-H equations, is also developed and the results are validated by experimental results. This study shows that the results of the panel method code have good agreement with experimental results, and that the maximum error of this code for the thrust and torque coefficients is 4% and 7%, respectively. The results of the FW-H noise code are also in good agreement with the experimental data.